1. Field of the Invention
The present invention relates to an amplifier using sigma-delta modulation, and more particularly, to an amplifier circuit and a related method for suppressing a mismatch error of feedback components according to logic levels of input voltages.
2. Description of the Prior Art
Recently, sigma-delta modulators have been widely used in amplifiers. Generally speaking, a one-bit quantizer is adopted in the sigma-delta modulator, wherein the one-bit quantizer generates a two-level output signal (i.e., −1 and 1). However, in some applications (such as audio amplifiers), the output signal of the quantizer toggles between −1 and 1 unceasingly even though its output power is quite low. Consequently, not only the efficiency of the amplifier is reduced, but also a large-scale LC filter is required to solve this issue. Since the present electronic products must satisfy the requirements of thin, light, and power-saved, there is no surplus space to contain the large-scale LC filter.
In order to solve the aforementioned problem, a middle level can be inserted in between the two-level output signal and the output signal of the quantizer can be transformed from two levels into three levels. However, feedback components on the feedback paths are not completely identical due to the manufacturing process issue. As a result, the mismatch error between the feedback components causes errors at the middle level, which affects the accuracy of the whole system.